Tag: fragmentation

European XFEL celebrates a successful restart

European XFEL celebrates a successful restart

European XFEL today celebrated the restart of the world’s largest X-ray laser with a ceremony attended by Hamburg’s Senator for Science Maryam Blumenthal and Guido Wendt, State Secretary in Schleswig-Holstein’s Ministry of Education, Science, Research and Culture. This was preceded by a so-called Long Installation and Maintenance Period (LIMP) with maintenance work and numerous upgrades to the infrastructure in underground tunnels and the scientific instruments on the European XFEL campus.

Employees of European XFEL and DESY, who were significantly involved in the extensive work, watched as Blumenthal and Wendt started the electron accelerator with a click of a mouse. Electron packets now speed again through the accelerator section to the so-called dump after about two-thirds of the 3.4-kilometre-long facility. The remaining parts of the X-ray laser, where the X-ray light is generated using the accelerated electrons, and the experiment stations will go into operation in the coming days and weeks. After more than seven months, the facility will be available to researchers again from mid-April.

Innovations for scientific excellence

At the ceremony in the Lighthouse visitor centre, European XFEL Managing Director Prof. Thomas Feurer emphasized the importance of the modification and upgrade work for the long-term performance, reliability and scientific excellence of the large-scale research facility. In addition to the successful maintenance work, for which the accelerator, which normally operates at minus 271 degrees Celsius, was warmed to room temperature and then cooled down again, teams from European XFEL and the DESY research centre installed numerous technical innovations to further expand the research options at the X-ray laser. Important upgrades include the new GUN5 electron source, which enables a pulse rate that is around 30 percent higher, and the expansion of beamlines and instruments for attosecond experiments, which can be used to observe ultrafast processes such as the formation of chemical bonds. In addition, preparatory work has been completed for the installation of superconducting undulators, which will deliver particularly short and highly intense X-ray pulses with very short wavelengths, enabling researchers to achieve even better resolution, among other things.

Read more on the European XFEL website

Image: Thomas Feurer emphasized the smooth cooperation between European XFEL and DESY, involving many teams from different disciplines.

Credit: European XFEL

Study Reveals Reversible Assembly of Platinum Catalyst

Study Reveals Reversible Assembly of Platinum Catalyst

UPTON, N.Y. — Chemists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory, Stony Brook University (SBU), and their collaborators have uncovered new details of the reversible assembly and disassembly of a platinum catalyst. The new understanding may offer clues to the catalyst’s stability and recyclability. The work, described in a paper just published in the journal Nanoscale, reveals how single platinum atoms on a cerium oxide support aggregate under reaction conditions to form active catalytic nanoparticles — and then, surprisingly, fragment once the reaction is stopped.

Fragmentation may sound shattering, but the scientists say it could be a plus.

“Such reversible fragmentation of a platinum nanocatalyst on cerium oxide could be potentially useful for controlling the catalyst’s long-term stability,” said Anatoly Frenkel, a chemist at Brookhaven Lab and professor at SBU who led the research.

When the platinum atoms return to their starting positions, they can be used again to remake active catalytic particles. Plus, the post-reaction fragmentation makes those active particles much less likely to fuse together irreversibly, which is a common mechanism that ultimately deactivates many nanoparticle catalysts.

“Part of the definition of a catalyst is that it helps disassemble and reassemble reacting molecules to form new products,” Frenkel noted. “But it was shocking to see a catalyst that also assembles and disassembles itself in the process.”

The paper describes how the scientists observed the nanoparticles forming as single platinum atoms aggregated on the cerium oxide surface at 572 degrees Fahrenheit (300 degrees Celsius) — the temperature of the reaction they were studying.

“After the reaction, we expected that these nanoparticles would stabilize once back at room temperature in whatever particle size they reached when they were activated,” Frenkel said. “But what we observed was a reverse process. The particles began fragmenting into single atoms again.”

The team had a hypothesis to explain what they were seeing, which was confirmed by thermodynamic calculations performed by theory colleagues at Chungnam National University in Korea. Carbon monoxide, one of the products of the reaction — often considered a “poison” for catalysts — was actively tearing the nanoparticles apart.

“Carbon monoxide molecules have a very strong repulsive interaction when they are next to each other,” Frenkel explained. During the “reverse water gas shift” reaction, which converts carbon dioxide (CO2) and hydrogen (H2) into carbon monoxide (CO) and water (H2O) at high temperatures, the CO typically leaves the catalyst surface as a gas. But once the heat is turned off, the CO molecules bind strongly to the platinum atoms of the catalyst. This brings the CO molecules closer to each other as the system cools down and their numbers rise.

Read more on BNL website

Image: Scientists have shown that platinum atoms (gold spheres) on cerium oxide (red and silver/black surface) can assemble into active nanocatalysts under reaction conditions and then disassemble when cooled down before reuse. 

Credit: Valerie Lentz/Brookhaven National Laboratory